Should You Put Rocks at the Bottom of a Planter? A Horticulturist Weighs In

Putting rocks at the bottom of planting soil is kind of a hot topic in the gardening world: Some claim that it provides drainage benefits while others say it can actually hurt your plants. We all just want the very best for our little plant babies, so we asked a horticulturist to help clear the air and confirm whether or not you should put rocks at the bottom of your planter. 

Should You Put Rocks at the Bottom of a Planter?

The practice of putting rocks at the bottom of a planter comes from the belief that it adds drainage—that water will pool down between the rocks without swamping the potting soil and leading to root rot. But according to Justin Hancock, a horticulturist at Costa Farms, “A layer of rocks at the bottom of the pot isn’t as helpful as a lot of people think it is, and it can actually impede drainage a bit.” Adding a layer of rocks makes your soil shallower—slowing drainage—when really you should aim for a taller layer of soil. This will help with drainage naturally. 

“The idea that rocks create a barrier between the soil and sitting water isn’t accurate; since most potting mixes are made of fine particles that act like a sponge when the particles are together, these fine particles will filter down between the rocks and pull any sitting water up to the plant roots,” he says.

How to Improve Plant Drainage

All in all, Hancock confirms that it’s not necessary to put anything, especially rocks, at the bottom of your planter. Filling it with potting mix is all you need for most potted plants, just make sure the pot is large enough and the soil layer is tall enough. If you’re trying to fill some space in a large pot while keeping it light, Hancock recommends trying empty plastic bottles. 

To ensure that your plant has enough drainage, check that there is a hole at the bottom of your pot, which will allow excess water to escape and the roots to remain somewhat dry. If your pot doesn't have a drainage hole, you can use a power drill to add one yourself or repotting your plant into one with a hole. You can also use two pots—stack one with a hole inside of one without.

If you use rocks to keep soil from spilling out or insects from crawling into the holes at the bottom of your planter, Hancock suggests placing some kind of screen, netting, or even a coffee filter at the base for protection.